1. Field of Invention
The present invention relates to a backlight module. More particularly, the present invention relates to a light emitting diode.
2. Description of Related Art
A back light module is one of the most important parts of a liquid crystal display (referred to as LCD). Since the liquid crystal is not the luminous body, the LCD panel is illuminated by the back light module. The back light module typically includes a light source, a light guide plate and many optical films such as diffuser. Among all kinds of light sources of the back light module, the light emitting diode (refer to as LED) has gradually become the most popular light source because it has the properties of the high brightness, long lifetime, small size, and low energy consumption. Nowadays, the luminous intensity of the LED has been improved, which means the desired luminance of the backlight module can be achieved with fewer LEDs. The utilization of fewer LEDs lowers the cost of the backlight module. However, when fewer LEDs are used, the gaps among LEDs are wider. If the light emitted from the LED is not strong enough to illuminate the wider gap, a dark line may be formed on the light guide plate corresponding to the gap area, and furthermore, non-uniform light may be provided to the LCD panel. In addition, if the large angle of the light emitted from the LED can not be increased as the gap space increased, the dark line on the light guide plate would become more obvious, which may lead to the panel with non-uniform brightness also. In other words, it is difficult to handle the panel with uniform brightness and reduce the quantity of the LED at the same time.
In addition, electronic devices are becoming thinner and lighter, so it is necessary to thin the LCD as well. As the LCD becomes thinner, the backlight module and the light guide plate thereof also become thinner. When the thickness of the light guide plate is almost as small as the thickness of the LED, the angular distribution of light field of the LED in the vertical direction may be too broad and some of light may leak out from the light guide plate, which may lead to light leakage problems.
Therefore, a new backlight module and a new LED thereof are necessary. The new LED may have different angular distribution of light field in different directions. In a horizontal direction, the light field should be strong enough at a large angle to prevent generating dark lines. In the vertical direction, the light field should be limited to small angles to ensure that each light beam is incident on the light guide plate to prevent light leakage problems.